The disclosed methods and apparatus generally relate to methods and apparatus for electrical power distribution and metering systems and, more particularly, to meter centers comprising digital electronic meter assemblies.
Conventionally, electric power consumption within residential or commercial buildings (and consumed by individual units located therein) is measured using electromechanical watt-hour meters. Although there are several different types of watt-hour meters in widespread use today, each typically essentially comprises a small electric motor and a counter. A precise fraction of the current flowing in the circuit is diverted to operate the motor. The speed at which the motor turns is proportional to the current in the circuit, and, therefore, each revolution of the motor's rotor corresponds to a given amount of current flowing through the circuit. The counter is coupled to the rotor and adds and displays the amount of power the circuit has carried based on the number of revolutions of the rotor.
Conventional watt-hour meters, typically those electromechanical watt-hour meters having spinning discs, are being replaced by utility companies with digital meters (also referred to, for example, as “digital watt-hour meters,” “electronic meters,” or “digital electronic meters”). Digital meters typically sample voltage and current flowing through the meter thousands of times a second. An electronic circuit uses the sampled values to calculate root mean square (RMS) voltage, RMS current, Volt-Amps (VA), power, power factor (PF), and kilowatt-hours. The simple model displays that information on a display, such as a liquid crystal display (LCD). More sophisticated models retain the information over an extended period of time and can transmit the information to field equipment or a central location.
For example, digital meters can automatically transmit the amount of electric power consumed by a user to a power provider. In this way, the meter advantageously does not need to be manually read. High-end digital meters can be equipped with a range of communication technologies, including the following: Low Power Radio (LPR), Global System for Mobile Communications (GSM), General Packet Radio Service (GPRS), Bluetooth, and Infrared Data Association (IrDA), and the conventional Recommended Standards—RS-232 and RS-485—wired link technologies. Such meters are able to store entire usage profiles with time stamps and relay them at a click of a button. Demand readings stored together with the profiles accurately indicate customer load requirements. The load profile data is processed by the utility company and renders itself adaptable to a variety of representations, graphs, reports, and the like.
Meters can also be read manually or using semi-automated technology. Often, meters designed for semi-automated reading include a serial port. The serial port communicates via an infrared light-emitting diode (LED) that is positioned through the faceplate of the meter. In some apartment buildings, a similar protocol may be used. However, a wired bus using a serial current loop is typically used to couple all the meters to a single plug. The plug is often located proximate mailboxes in the building.
Sub-metering comprises the resale of electricity or allocation of costs within a multi-unit site. Meter centers have been used to facilitate sub-metering. Meter centers including a plurality of socket-type meters are commonly used to distribute electricity to and measure electric power consumed by, for example, the various tenants of a multi-unit residential site (e.g., without limitation, an apartment building) or commercial site (e.g., without limitation, an office complex). Depending on their configuration, meter centers may also be referred to, for example, as “multiple metering stacks,” “gangable (or expandable) metering stacks,” and “group metering stacks.”
Individual watt-hour meters typically plug into standardized sockets in North American meter centers by clamping of stabs on a meter with jaws of a corresponding socket. While this permits meters to be replaced without disturbing wires coupled to the sockets, it negatively impacts the ability to easily replace or update the types of meters that are used in existing meter centers. While digital socket-type meters have been developed for retrofitting in conventional meter centers (e.g., see U.S. Pat. No. 4,804,957, several solid-state meters sold by Itron Inc. (Liberty Lake, Wash.), and the “S-20” solid-state socket meter available from Quadlogic (Long Island City, N.Y.)), improvements in this regard are still needed. For example, clamping of meters into meter sockets typically does not provide as secure of an electrical connection as is provided by other coupling apparatus and methodology, resulting in more likely malfunction of, tampering with, or even theft of the meter.
FIGS. 1 and 2 illustrate a prior art meter center 1 assembly, which generally consists of a cabinet 3 having an internal longitudinal wall 5 that divides the cabinet 3 into side-by-side meter and disconnect switch compartments 7, 9. A plurality of plug-in, socket-type watt-hour meters 11 are mounted within the meter compartment 7, one meter 11 for each tenant circuit to be metered. Thus, in the example of FIG. 1, the meter center 1 accommodates four tenant circuits each served by its own meter 11. Each tenant circuit is also provided with a disconnect switch 13 such as, for example, a circuit breaker, which is mounted within the disconnect switch compartment 9. Electric power is provided to the meter center 1 by feeder buses 17 that are electrically coupled to utility lines (not shown) for power supply. Specifically, as shown in FIG. 2, three differently phased feeder buses 17A, 17B, 17C and a neutral feeder bus 17N extend horizontally through the cabinet 3 for electrical connection to the utility lines. A set of supply buses 27 extends vertically within the meter compartment 7 for electrical connection to the feeder buses 17. More specifically, the supply buses 27 generally comprise a pair of spaced apart bus bars 29R, 29L, which are each electrically coupled to one of the feeder buses 17A, 17B, 17C by a phase balancer 47A, 47B. For example, the left supply bus bar 29L in the example of FIG. 2 is electrically coupled to the phase A feeder bus 17A by phase balancer 47A, and the right supply bus bar 29R is electrically connected to the phase B feeder bus 17B by phase balancer 47B. Phase balancer 47A generally consists of a cylindrical sleeve 49 (shown in hidden line drawing) and bolt 51. Phase balancer 47B generally consists of a “Z”-shaped member 53 and bolts 55. Thus, the entire meter center 1 is configured in the same manner, in this case phase A-B, although it will be appreciated that it could also be entirely phased A-C (using feeder phase buses 17A and 17C) or B-C (using feeder buses 17B and 17C) or different meters within the same cabinet can be phased differently (e.g., on two different phase combinations, such as A-C and B-C).
Other systems and methods of sub-metering are known. See, for example, U.S. Pat. Nos. 4,575,801; 4,783,748; 4,804,957; 6,947,854; and 7,252,543. Not all of these other systems and methods of sub-metering employ meter centers as defined herein. For example, the systems and methods described in U.S. Pat. No. 7,252,543 do not employ such meter centers and are limited in the number of units that can be sub-metered. Similarly, see Eaton Corporation's Cutler-Hammer PRC Tenant Meters, such as the PRC7000/PRC7500 Tenant Metering systems available from Eaton Corporation (Moon Township, Pa.). In addition, Square D by Schneider Electric (LaVergne, Tenn.) supplies metering products under the POWERLOGIC® trade name and meter centers employing socket-type meters under the Square D EZ Meter-Pak® trade name. Siemens Energy and Automation, Inc. (Alpharetta, Ga.) also supplies a variety of socket-type meter stacks for multi-family metering. In addition, Quadlogic (Long Island City, N.Y.) supplies a variety of metering products. For example, the “MiniCloset-5” (two coupled enclosures, each having dimensions of about 13.5 inches by 8.5 inches by 4.5 inches, with one enclosure housing a “MiniCloset Interface Board” and the other housing a data collector) and “MiniCloset-5c” (one enclosure for all components, the enclosure having dimensions of about 18 inches by 10 inches by 6 inches) multi-tenant meters are sold by Quadlogic for the monitoring of up to twelve two-phase residential customers or up to eight three-phase commercial customers. The technical specifications for these meters state that 0.1 Amp and 5 Amp current input models are available. As such, these metering products are generally not able to distribute power directly from a utility line. Rather, these meters are constructed to be used in conjunction with and require a distinct power distribution panel as illustrated in technical literature on Quadlogic's internet website.
Despite the availability of certain metering products and meter centers, there is need for improvement in methods and apparatus for electrical power distribution and metering. Particularly desirable are improved methods and apparatus for sub-metering with the use of “gangable metering stacks.” The present disclosure describes such improved methods and apparatus.